New graphene-based supercapacitors rival lead-acid batteries

August 5, 2013

SEM image of graphene/ionic liquid hybrid film (credit: Yufei Wang)

Monash University researchers have developed a completely new strategy to engineer graphene-based supercapacitors (SC), making them viable for widespread use in renewable energy storage, portable electronics and electric vehicles.

SCs are generally made of highly porous carbon impregnated with a liquid electrolyte to transport the electrical charge. Known for their almost indefinite lifespan and the ability to re-charge in seconds, the drawback of existing SCs is their low energy-storage-to-volume ratio — known as energy density.

Low energy density of five to eight Watt-hours per liter means SCs are unfeasibly large or must be recharged frequently.

Professor Dan Li’s team has created an SC with energy density of 60 Watt-hours per liter (0.06 Watt-hours cm-3) — comparable to lead-acid batteries and around 12 times higher than commercially available SCs.

“It has long been a challenge to make SCs smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses,” Professor Li said.

Graphene, which is formed when graphite is broken down into layers one atom thick, is very strong, chemically stable and an excellent conductor of electricity.

To make their uniquely compact electrode, Professor Li’s team exploited an adaptive graphene gel film they had developed previously. They used liquid electrolytes — generally the conductor in traditional SCs — to control the spacing between graphene sheets on the sub-nanometer scale. In this way the liquid electrolyte played a dual role: maintaining the minute space between the graphene sheets and conducting electricity.

Unlike in traditional “hard” porous carbon, where space is wasted with unnecessarily large pores, density is maximized without compromising porosity in Professor Li’s electrode.

To create their material, the research team used a method similar to that used in traditional paper making, meaning the process could be easily and cost-effectively scaled up for industrial use.

“We have created a macroscopic graphene material that is a step beyond what has been achieved previously. It is almost at the stage of moving from the lab to commercial development,” Professor Li said.

I understand your point about variable capacitors to perform voltage conversion, but I don’t think it would be economically feasible to do so. But I don’t understand what you mean about
“‘children’ watching.”

Super-capacitors use an electrolyte rather than dielectric. The wikipedia article on supercapitors/ultracapitors helps to explain. This does not make them batteries, rather the charge seperation of conventional capacitors can be acheived at the level of individual ions experiencing adhesion to a large surface.

..thanks in advance for trying to track down a volumetric value related to the energy density and update this article. Everyone would benefit from a Moore’s law like improvement to battery charge times, reduction in size, drop in cost, etc. I am always curious if electric cars are pushing these advancements, or if much smaller devices like cell phone and tablets are pushing this technology the most?

It could be both cars and portable electronics that are driving the development of supercapacitors and super batteries.

But what does it matter!

These batteries will lead in so many technological advances. Just imagine what they will do for robots on the moon.

After 3-D printed robots can be made, robots can soon double their numbers on the moon.

There are traces of carbon around the craters made by carbonaceous asteroids, so graphene and carbon nanotubes can be fabricated there.

Once a large number of robots are operating there, they can pick up their solar arrays and install them on the tops of the sunny rims of those craters at the lunar south pole with all the ice down in their dark bottoms.

Nickel-iron from all the micro-meteoroids that have been peppering the moon-dust for billions of years can be used to make power lines to stretch down to the bottoms of the craters.

Then the robots can go down in the mines to cut out blocks of ice, then climb up to stack the blocks and recharge at the same time.